The invention relates to a method for determining the orientation and the position of an object, in particular, a body implant, in space, with the assistance of a sensing instrument provided with a marking element and thereby determinable with respect to its orientation and its position by means of a navigation system.
Navigation systems for detecting the position of special marking elements in space are known. This position, i.e., the position in space and the orientation in space, may be determined in various ways. For example, the marking elements may have several spatially separate radiation sources or reflectors which direct radiation onto several likewise spatially separate radiation receivers, so that the position of the marking elements may be determined on the basis of the different propagation times and/or on the basis of the different orientation of the direction of emission. There are quite a large number of such navigation systems with different working mechanisms which can all be used for this purpose. The marking elements are normally directly rigidly connected to objects whose position in space is to be determined.
However, this is not possible in all cases, for example, in the case of body implants which have to be inserted through narrow openings into the body. In the case of such implants and also other objects whose position is to be determined, this determining of the position can also be carried out with the assistance of sensing instruments which are rigidly connected to a marking element whose position can be detected by the navigation system. These sensing instruments can be applied in a certain way to the objects so that the position of the object can thereby be determined, for example, by point-by-point scanning.
It is also known to make defined, in particular, conical recesses on objects for insertion of the sensing instrument therein with a sensing tip. The lowermost point of such a recess can be determined with respect to its position by moving the sensing instrument on a cone, and the position of the object in space can then also be determined from several such recesses on an object. However, this method requires the recesses to be freely accessible for a sensing instrument and, in particular, for the sensing instrument to be able to be moved freely for movement within a cone in the recess. Therefore, this possibility must also be ruled out when the objects are only accessible to a limited extent, for example, when implants are implanted inside the body.
In principle, it would also be possible to join these implants to a marking element by way of an extension and to thereby determine the position of the implant. As a rule, however, the distance between the implant and the marking element is relatively large since the implant is inserted inside the body and the marking element must be arranged outside the body. There is, therefore, the danger that the extension or connection fixing the marking element to the object will undergo deformation, which will result in erroneous measurements. Even a slight bend in such an extension can result in deviations of several degrees in the determining of the orientation.
The object underlying the invention is to so configure a method of the kind described at the outset that the position of an object can be precisely and simply determined without having to establish a rigid connection between marking element and object and without free accessibility to the object from all sides being required.